The invention relates to a device for checking letter-mail.
A known checking device developed for said purpose by Tokyo Shibaura Electric Co. Ltd. in Japan is adapted to check if the letters which are supplied to said checking device via a conveyor contain a hard object. For this purpose the latter checking device is provided with four cylindrical rollers, which are coaxially arranged in line and level, and which are each tiltably supported independently of one another. The axes of rotation of these rollers extend in a cross direction along a pair of conveyor belts of a letter-mail conveying device, which conveyor belts run parallel and are located in the same plane. A supporting roller is arranged adjacent to the sides of said conveyor belts which do not face the rollers, in such a way that said supporting roller will be in a position opposite to the aforesaid four rollers. By means of a special spring mechanism each of these rollers, which act as scanners, is pressed against the conveyor belts, which in their turn are pressed against said supporting roller. Each of said scanning rollers is coupled to a shutter adapted to interrupt a bundle of rays directed to a photosensitive detector, when the appurtenant scanning roller of the convevyor belt is tilted away. In the case when a letter on the conveyor belts has a thickened and hardened part, in such a way that relevant scanning roller is tilted away from the conveyor belts against the spring force exerted on such roller, and said bundle of rays is interrupted by the shutter, the detector will produce a signal to indicate that a letter does not meet the requirements. A device of this kind has the drawback that it can only be investigated if a letter supplied to this device contains a hard object which causes a local thickening to such an extent that it is unacceptable for a further letter-mail handling. Because of such a limited checking possibility this known technique cannot be used as an input check for automatic letter-mail handling machines in which letters have to pass switches which have been constructed especially for high speeds. The constructive embodiment of such machines imposes certain restrictions with regard to thickness, stiffness and weight on the letters that have to be handled. The machine handling can be disturbed e.g. if a letter contains an object of such a length and stiffness, e.g. a ballpoint pen, that it cannot pass through a bend occurring in the handling path of the machine. Disturbances in the working or damages to the machine can further be caused if the contents of a letter meet the requirements with regard to stiffness and thickness, but the weight of which is larger than a fixed upper limit value. Such disturbances involve that the machine has to be stopped, which with the high handling speeds leads to unacceptable disturbance frequencies already when the "contents-to-be-rejected" percentages are apparently small. When the contents of e.g. 1 out of every 1000 letters have to be rejected, this results in 30 disturbances (machine stops) on an average by the hour, which is unacceptable in connection with the requirements for the quality of service and for cost control.
A further drawback of the aforesaid known device is that the constructive embodiment is relatively complicated and vulnerable. Moreover, the setting of the separate spring mechanisms and stop pins is timeabsorbing and needlessly complicated.